Method of rigidly securing members with a recessed fastener

ABSTRACT

An elongated strip of bead stock is secured to a sheet metal draw die by first punching longitudinally spaced tapered holes within the strip with a punch having a diameter substantially smaller than the opening within the punch die. The strip is shaped and inserted within a groove formed within the draw die, and a pin-like fastener is inserted through each tapered hole and into a correspondingly aligned blind bore formed within the draw die. The outer end of each fastener is peened so that it expands both within the bore adjacent a hardened ball placed within the bore, and also within the tapered hole to effect a rigid and positive connection between the bead stock and the forming die. A punch tapered hole and a recessed tapered head fastener are also disclosed for rigidly connecting other adjacent members.

United States Patent Hicok Nov. 7, 1972 Hershel E. Hicok, 4636 PineVillage Drive, Orchard Lake, Mich. 48033 Filed: May 14, 1970 Appl. No.:37,249

Inventor:

References Cited UNITED STATES PATENTS 5/1905 Dodge ..29/522 UX 3/ 1942Leighton ..29/522 UX 9/1970 Pipher ..29/522 X 10/1932 Groehn ..72/35010/1940 Oeckl et al ..29/522 UX FOREIGN PATENTS OR APPLICATIONS 934,6155/1948 France ..29/522 Primary Examiner-Charlie T. MoonAttorney-Marechal, Biebel, French & Bugg [57] ABSTRACT An elongatedstrip of bead stock is secured to a sheet metal draw die by firstpunching longitudinally spaced tapered holes within the strip with apunch having a diameter substantially smaller than the opening withinthe punch die. The strip is shaped and inserted within a groove formedwithin the draw die, and a pin-like fastener is inserted through eachtapered hole and into a correspondinglyaligned blind bore formed withinthe draw die. The outer end of each fastener is peened so that itexpands both within the bore adjacent a hardened ball placed within thebore, and also within the tapered hole to effect a rigid and positiveconnection between the bead stock and the forming die. A

punch tapered hole and a recessed tapered head fastener are alsodisclosed for rigidly connecting other adjacent members.

6 Claims, 7 Drawing Figures PATENTEDnuv 1 ma 4 3,702,085

IN VE N TOR HERSHEL E. HICOK MM, M7843 A TTOR/VE Y5 METHOD OF RIGIDLYSECURING MEMBERS WITH A RECESSED FASTENER BACKGROUND OF THE INVENTION Inthe art of constructing a die for drawing sheet metal, as for example, adie which is used for producing an automobile panel, it is common tomount a shaped strip of head stock on either the female die or on theblank holding die which surrounds the punch or male die. The stripextends generally arOund the die cavity and has a rounded projectingsurface which is adapted to extend into a complementary shaped recess orgroove formed within the opposing die. The bead material is usuallyformed of steel having a hardness range that could vary from soft toharder than that of the die proper and functions primarily t minimizewear on the dies and to minimize the formation of wrinkles within themetal sheet aS it is being drawn.

Sometimes a rounded bead strip is formed as an integral part of thefemale die or blank holding die, but usually the strip is formed frombead stock having a D- shaped cross-sectional configuration. After thestrip of bead stock is formed to the desired configuration correspondingto the shape Of the die cavity, the strip aS inserted into acorrespondingly shaped groove and is secured by a series oflongitudinally spaced fasteners.

The fasteners may comprIse cap screws which extend through holes drilledand counterbored within the bead stock and are threaded intocorresponding holes formed within the die. It is also common to drill aseries of holes within the bead stock and then taper ream each hole forreceiving a pin-line fastener which is inserted into a correspondinglyaligned hole within the die. The outer end portion of the pin-likefastener is peened to expand the fastener within the tapered hole in thebead stock, after which the fastener is ground or filed so that its endsurface is flush with the curved or rounded surface of the bead stock.

Due to the substantial number of fasteners which are required, atintervals of a few inches, to secure a-strip of bead stock to a die, ithas been found that substantial time isrequired for drilling holeswithin the bead stock and for counterboring or taper reaming each hole.For example, it is not uncommon for the drilling and reaming operationsfor each hole to require 6 or 7 minutes. This time significantlyincreases the cost of attaching the bead stock to a die and thussignificantly increases the overall cost of the die set.

SUMMARY OF THE INVENTION The present invention is directed to animproved method of securing two members together with a recessedfastener extending through or into aligned holes formed within themembers. The method of the invention is particularly suited for securinga strip of head stock to a metal drawing die. According 'to thepreferred method of the inVention, a series of longitudinally spacedtapered holes are punched within a strip of bead stock by successivelyadvancing the strip between a cylindrical punch having a diametersubstantially smaller than the diameter of a hole formed within thepunch die. As a result of this differential diameter, a tapered hole,defined by a frusto-conical surface, is formed within the bead stock,and the larger end of the hole is located adjacent the rounded surfaceof the bead stock.

After the strip of bead stock is formed to the desired configuration, itis inserted within a complementary shaped groove formed within the drawdie, and blind holes are drilled within the die in allgnment with thetapered holes in the bead stock. A cylindrical pin-like fastener isinserted into each of the holes after a hardened steel ball is locatedat the inner end of the hole. The outer end portion of the fastener ispeened so that it expands into the tapered hole within the bead stockand the inner end portion of the fastener expands within the hole aroundthe ball to form a rigid connection between the bead stock and the die.The method of the invention may also be used for forming a non-circularhole within a member to prevent rotation of a fastener which is expandedor fitted into the hole.

A primary advantage provided by the invention in the art of die makingis the significant time savings in forming the tapered holes within thebead stock when compared with the prior method of drilling, taperreaming and deburring each hole. However, other advantages and featuresof the invention will be apparent from the following description, theaccompanying drawing and the appended BRIEF DESCRIPTION OF THE DRAWINGFIG. 1 is a somewhat diagrammatic fragmentary section of a draw die setincorporating a strip of bead stock formed and secured in accordancewith the invention;

FIG. 2 is a view illustrating the punching of the bead stock to form atapered hole in the stock; I

FIG. 3 is a fragmentary section of a die illustrating the assembly ofthe bead stock;

FIG. 4 is a view similar to FIG. 3 and showing the bead stock after ithas been secured to the die;

FIG. 5 is an enlarged fragmentary section of the lower portion of theassembly shown in FIG. 4;

FIG. 6 is a fragmentary section of two adjacent members rigidlyconnected in accordance with the present invention; and

FIG. 7 illustrates a subsequent counterboring operation which may beperformed on the bead stock in accordance with the invention.

DESCRIPTION OF THE PREFERRED METHOD OF THE INVENTION FIG. 1 showsdiagrammatically a die set for drawing a blank or sheet S of metal andwhich generally includes a female die 10 defining a cavity 12 withln ablank supporting surface 13. A punch or male die 14, having aconfiguration corresponding to that of the cavity 12, is slidablysupported within a blank holding die or blank holder 15 having a lowersurface 16 adapted t0 move downwardly toward the surface 13 of thefemale die 10. An elongated strip 20 lower bead stock surrounds thepunch 14 and is mounted within a corresponding groove 22 formed withinthe bottom surface 16 of the blank holder 15. Preferably, the strip 20has a D-shaped cross-sectional configuration forming a rounded bottomsurface 24 which is adaPted to project into a complementary shapedrecess 25 formed within the upper blank holding surface 13 of the die 10and extending around the cavity 12.

Referring to FIGS. 2-5, the strip 20 of head stock is preferably formedof cold rolled steel or SAE 10-18 or 10-20 steel having a Rockwellhardness in the low thirties, although the bead stock may be composed ofa pretoughened alloy steel. A series of longitudlnally spaced taperedholes 28 are formed within the strip 20, and each hole is defined by afrusto-conical surface 30 extending from a substantially cylindricalsurface 32. The tapered holes 28 are preferably spaced at intervals ofbetween 2 and 8 inches depending uponthe particular application of thedie, and have a taper angle A (FIG. 3) of between 6 and 8.

In accordance with the presentinvention, each of the tapered holes 28 isformed within the strip 20 of bead stock by progressively advancing thestrip 20 between a cylindrical punch 35 (FIG. 2) and a die 36 having acylindrical opening or bore 38. The bore 38 extends downwardly fromthe-bottom of a cavity 39 which has a cross-sectional configurationcorresponding to that of the strip 20 of bead stock. The punch 35 has adiameter substantially smaller than the diameter of the bore 38 so thatwhen the punch 35 is pressed or forced through the strip 20, it removesa tapered slug 42by shearing the strip along a generally frusto-conicalshear plane. This causes the formation of the'frusto-conical surface30'and the generally cylindrical surface 32 within the strip. Thediameter of the punch 35 and the diameter of the bore 38 are correlatedaccording to the size or thickness of the strip 20 to produce thecombination of the tapered surface 30 and the cylindrical surface 32 aswell as the taper angle A of between 6 and 8. The pressing of the punch35 into the strip 20 is also effective to form a small radius 44 at theupper end (FIG. 2) of the tapered hole 28, thereby eliminating the needfor deburring the punched hole after it is formed.

Referring t FIGS. 3 and 4, after the strip 20 of bead stock is punchedwith a series of longitudinally spaced tapered holes 28, the strip isformed according to the configuration of the groove 22 and is insertedinto the groove. A corresponding seriesvof blindbores or holes 45 aredrilled into the blank holder and extend from the bottom surface of thegroove 22in alignment with the tapered holes 28 within the strip of beadstock. A hardened steel. ball 46, such as a ball bearing, is placedwithin the bottom of each of the holes 45, and an elongated cylindricalfastener or pin 48 is inserted through each tapered hole 2 and into thecorresponding hole 45 until the inner end surface of the pin contactsthe ball 46 and the outer end surface projects slightly from the taperedhole 28.

The outer end portion of each pin 48 is peened with the aid of apneumatic hammer or by hand causing the portion to expand to form afrusto-conical head portion 49 which firmly engages the frusto-conicalsurface 30. The peening operation is also effective to deform the innerend portion of each pin 48around the spherical surface of the ball 46(FIG. 5) causlng the pin 48 is expand and conform to the minorirregularities of the hole. As a result, the pins 48 form a rigid andpositive connection between the strip 20 of bead stock and the blankholder 15. After the outer end portion of each pin 48 is peened to formthe tapered head portion 49, the head portion is ground down to asurface 51 which conforms to the surrounding cuRved rounded surface 24of the strip 20. I

Referring to FIG.'7, when it is desired to retain the strip -20 of beadstock by a series of longitudinally spaced cap screws (not shown) havinghexagonal recesses for receiving an Allen wrench, the strip 20 is firstpunched to form a series of tapered holes 28. Each of the tapered holesis then counterbored to form a radial annular shoulder 54 which isengaged by the head of the cap screw when it is inserted into an alignedthreaded hole formed within the blank holder 15. By first punching eachtapered hole 28 and then counterboring the tapered hole as shown in FIG.7, the counterbored holes can be formed in a much shorter period oftimethan was heretofore required for drilling and counterboring a hole.

In reference to FIG. 6, the method of the invention, which is describedabove for securing a strip 20 of head stock toa draw die, may also beused for rigidly joinlng or connecting any two adjacent members, as forexample, two metal plates 60 and 62. That is, the plate 60 is punched ina manner as Shown in FIG. 2 to form a tapered hole 64, and the late62 issimilarly punched to form a tapered hole 66. A fastener in the form of aflat tapered head rivet 68 is inserted into the holes 64 and 66 so thatthe head portion of the rivet is received within the tapered hOle 66.The opposite end portion of the rivet 68 is then peened vto form theexpanded head portion 69 which engages the surface defining the taperedhole 64. The rivet 68 thereby forms a rigid connection between theplates 60 and 62 without projecting above the outer surfaces of theplates. It is apparent that tapered holes need not be punched in both ofthe members or plates 62. For example, the plate 62 might be providedwith a tapped hole, and-a screw having a tapered head would be insertedinto the punched tapered holes 64 for rigidly connecting the members.

From the drawing and the above description, it is apparent that themethod of securing a strip of bead stock to a die member in accordancewith the invention provides desirable features and advantages. Forexample, by successively punching longitudinallyspaced tapered holeswithin the strip 20 of. bead stock, instead of drilling, taper reamingand deburring each hole, a significant amount of time is saved informing each hole. Thus in view of the substantial number of holesrequired for securing the bead stock to the die, the total time savedfor forming all of the tapered holes significantly reduces the overallcost of the die. As mentioned in connection with FIG. 7, the punching ofeach tapered hole 28 and then counterboring the larger end of the hole,also provides for significantly reducing the time for formingcounterbored holes in comparison to the prior method of drilling andcounterboring each hole. Another advantage of punching the tapered holesis obtained by the formation of the slight radius 44 at the outer endsof each hole. That is, the radiuS 44 eliminates the need for deburringthis end of the hole to assure that the strip 20 of head stock seatswithin the groove 22.

While the punching of the tapered holes 28 vand the use of a taperedheaded fastener is ideally suited for securing a Strip of bead stock toa draw die, as mentioned above in connection with FIG. 6, the method ofthe invention may also be used for joining any two members when it isdesirable to recess the head portion of a fastener either flush or belowthe surface of one of the members. As also mentioned above, it is withinthe Scope of the invention to punch a non-circular tapered hole within amember for securing the member to another member with a fastener whichis expanded or formed to fit within the non-circular hole so that it isprevented from rotating. Furthermore, while the method herein describedconstitutes a preferred embodiment of the invention, it is to beunderstood that the invention is not limited to this precise method, andthat changes may be made therein without departing from the scope of theinvention which is defined in the appended claims. I

What is claimed is:

1. An improved method of securing a strip of bead stock having agenerally D-shaped cross-section to a draw die having a groove forreceiving the fiat face of said strip, comprising the steps ofpositioning said strip adjacent a punch die with its curved face inward,said punch die having an opening of a predetermined diameter, selectinga-punch having a cross-sectional area substantially smaller than that ofsaid opening, pressing said punch through said strip to force a slug ofthe strip into said opening and to form a tapered surface defining atapered hole with its larger diameter opening on the curved face of saidstrip, mounting said strip on said draw die with its curved faceoutward, forming a bore within said draw die in alignment with said holein said strip, and attaching said strip to said draw die with a fastenerhaving a tapered head portion engaging said surface defining saidtapered hole and conforming the outer end of said fastener to thecurvature of said strip.

2. A method as defined in claim 1 including the step of forming agenerally cylindrical surface within said strip adjacent said taperedsurface during 'said punchinG operation by correlating the diameter of acylindrical said punch and the diameter of a cylindrical said openingwithin said punch die with the thickness of said strip.

3. A method as defined in claim 1 including the step of inserting a ballwithin said bore, inserting a pin-like said fastener into said bore withits inner end portion engaging said ball and its outer end portionprojecting into said tapered hole within said strip, and peening saidouter end portion of said fastener within said hole to effect expandingof said inner end portion of said fastener within said bore andexpanding of said outer end portion to form said head portion.

4. A method as defined in claim 1 including the step of counterboringsaid punched tapered hole to form a hole having an internal annularshoulder for receiving a fastener having a head portion adapted toengage said shoulder 5. A method as defined in claim 1 including thestep of successively advancing said strip between said punch and saidpunch die, and successively pressing said punch through said strip toform a plurality of longitudinally spaced said tapered holes within saidstrip.

6. A method as defined in claim 1 including the steps of counterboringthe larger end of said punched tapered hole to form an internal annularshoulder, and attaching said strip to said die with a fastener having ahead portion engaging said shoulder.

1. An improved method of securing a strip of bead stock having agenerally D-shaped cross-section to a draw die having a groove forreceiving the flat face of said strip, comprising the steps ofpositioning said strip adjacent a punch die with its curved face inward,said punch die having an opening of a predetermined diameter, selectinga punch having a cross-sectional area substantially smaller than that ofsaid opening, pressing said punch through said strip to force a slug ofthe strip into said opening and to form a tapered surface defining atapered hole with its larger diameter opening on the curved face of saidstrip, mounting said strip on said draw die with its curved faceoutward, forming a bore within said draw die in alignment with said holein said strip, and attaching said strip to said draw die with a fastenerhaving a tapered head portion engaging said surface defining saidtapered hole and conforming the outer end of said fastener to thecurvature of said strip.
 2. A method as defined in claim 1 including thestep of forming a generally cylindrical surface within said stripadjacent said tapered surface during said punchinG operation bycorrelating the diameter of a cylindrical said punch and the diameter ofa cylindrical said opening within said punch die with the thickness ofsaid strip.
 3. A method as defined in claim 1 including the step ofinserting a ball within said bore, inserting a pin-like said fastenerinto said bore with its inner end portion engaging said ball and itsouter end portion projecting into said tapered hole within said strip,and peening said outer end portion of said fastener within said hole toeffect expanding of said inner end portion of said fastener within saidbore and expanding of said outer end portion to form said head portion.4. A method as defined in claim 1 including the step of counterboringsaid punched tapered hole to form a hole having an internal annularshoulder for receiving a fastener having a head portion adapted toengage said shoulder
 5. A method as defined in claim 1 including thestep of successively advancing said strip between said punch and saidpunch die, and successively pressing said punch through said strip toform a plurality of longitudinally spaced said tapered holes within saidstrip.
 6. A method as defined in claim 1 including the steps ofcounterboring the larger end of said punched tapered hole to form aninternal annular shoulder, and attaching said strip to said die with afastener having a head portion engaging said shoulder.